In recent years, a head-up display apparatus is used to deliver various information on a vehicle such as a vehicle speed, a navigation information to a destination of a travel or the like. A conventional head-up display uses an image projection device for projecting an image on a windshield, and an image screen for receiving and displaying the image from the image projection device. Japanese Patent Document JP-A-2004-133181 discloses a head-up display apparatus that projects two different images from single image projection device onto two separate screens.
The head-up display apparatus described above uses an image display device and two triangular prisms. The image display device displays two separate images in one image display area. The image display device uses a transparent liquid crystal display (LCD) panel, and a light source for providing a light to the LCD panel. The image display device has an image separation panel for preventing interference of two images in the image display area. The triangular prisms are used to redirect two images on the LCD panel toward two separate optical paths. The triangular prisms are disposed on the image separation panel for respectively guiding each of the two separate images on the LCD.
The two separate image screen of the head-up display apparatus is used for displaying two separate images projected from the triangular prisms. The two image screens are respectively positioned in an instrument panel and on a windshield to display a speed meter and similar instruments. The two image screens display two separate images at the same time.
The head-up display apparatus splits a single frame of an image on the LCD panel into two images, and projects them onto two separate screens. That is, the two images on the LCD panel are respectively projected to the two triangular prisms to be redirected toward the two image screens. The two images pass along the two separate optical paths to be displayed on the two separate image screens respectively in the instrument panel and on the windshield. In this manner, a driver of the vehicle perceives the two separate images respectively in the instrument panel and on the windshield.
The images displayed on the image screen in the head-up display apparatus can be used to display various kinds of information such as vehicle information, navigation information, a night-vision image, and the like. The head-up display apparatus itself contributes to safety of driving operation because it minimizes driver's eye movement for collecting information by displaying the image on the windshield beside delivering various kinds of information.
However, the conventional head-up display apparatus cannot displays two different images on one image screen. That is, a head-up display apparatus that can deliver two different images at the same time on the windshield by using two optical paths has not been disclosed.
In addition, the two different images respectively include contents having different natures, or different characteristics. Therefore, the sizes and the positions of the two images on the windshield has to be differentiated.